Squamous cell carcinoma (SCC) is the second most common subtype of lung cancer and is responsible for over 40,000 deaths each year in the United States alone. SCC has a survival rate of 15% and unlike the other major subtype of lung cancer, there are currently no approved targeted therapies for SCC. Recently, The Cancer Genome Atlas sequenced 178 human SCCs and identified numerous genetic alterations that may serve as valuable therapeutic targets. Because SCC is highly associated with smoking, the genetic mutation rate is one of the highest of all tumor types, making it difficult to distinguish driver from passenger mutations. Clearly, a major unmet need for the treatment of SCC is the identification of new therapeutic targets and treatment strategies. The transcription factor Sox2 is one of the most commonly altered genes in SCC, amplified in 23% and overexpressed in 60-90% of human SCCs. However, Sox2's function and key target genes in lung SCC are unclear. In addition, there are currently no targeted therapies that inhibit this transcription facor. We recently developed a novel mouse model of SCC driven by Sox2 expression that highly resembles the human disease at the level of histopathology, biomarker expression and pathway activation. This model will be a useful tool to identify novel therapeutic targets and biomarkers, elucidate mechanisms of tumor progression, identify the cell(s) of origin, and test novel therapies and drug combinations in SCC. The objective of this study is to use this novel mouse model and human lung cancer cells to identify pathways critical for Sox2-driven SCC and to elucidate the cell(s) of origin for SCC in vivo. We hypothesize that mouse tumors (since not exposed to carcinogen) will have fewer genetic alterations than the human disease and thereby serve as a biological filter to identify important pathways driven by or cooperating with Sox2. Based on preliminary in vitro and in vivo data, we predict that Sox2 drives targetable pathways that are critical for tumor initiation and/or maintenance. Given that Sox2-driven SCCs express markers of basal cells, we predict that Sox2 either arises in basal cells or transforms other lung cell types to a basal cell identity. To test these hypotheses, we will: 1) use next-generation sequencing to identify conserved genetic changes between mouse and human SCC, 2) test the impact of inhibiting key pathways in Sox2-expressing human lung cancer cells, and 3) use our bicistronic lentiviral system with cell type-specific promoters to determine which lung cell type functions as the cell(s) of origin for Sox2-driven SCC in vivo. This approach is innovative because we will employ a novel mouse model of SCC that highly recapitulates the human disease. This research is significant because lung cancer is the leading cause of cancer death in the United States and there are currently no targeted therapies approved for SCC. A better understanding of the critical pathways and cellular origins of SCC will impact the treatment and survival of patients with this intractable disease.